Method of testing steel



Dec. 5, 1933. L. E. HOWARD 1,937,820

METHOD OF TESTING STEEL Filed Dec. 17, 1929 azigfa Patented Dec. 5, i933taster METHOW Q3 TESTING STEEL Leslie E. Howard, lLockport, N. ii,assignor to Simonds Saw and Steel Company, Fitchburg,

Mass, a corporation of Massachusetts Application December It, 1929Serial Na. nieces This invention relates to a method for the detectionof soft spots in steel which has been subjected to heat hardeningtreatments.

It is well known in the steel industry that when 5 a casting or anyother kind of steel product is subjected to heat treatment for hardeningthe same, portions of the article may remain relatively soft, eventhough the remainder of the article has been hardened to the maximum demgree required.

Heretofore, it has been customary to inspect such products by etchingthe surface with acids of various kinds (such as hydrochloric orsulphuric) to dissolve the superficial coating of oxide which ordinarilydevelops in the course of manufacture and thus enable one to detectirregularities, which may have been developed, by the character of the.etching action of the acid. Some experience is required to interpretthe re- 0 sults observed and the method involves the consumption of aconsiderable quantity of acid, together with the inconvenience of thenecessity of washing and drying each article after its examination. Thepresence of acid in a shop is of itself undesirable, if it may beavoided.

Accordingly, it is an object of this invention to provide a methodwhereby the soft spots occurring in a hardened steel product of any kindmay be clearly revealed and positively identified, without requiringmore thancasual instruction of the operator and without necessitatingthe use of chemical reagents. Other objects will appear from thefollowing disclosure.

It is found, as a part of the present invention, 5 that the surfaces ofhardened steel objects may be uniformly and completely cleaned, whetherrough or smooth, and whether containing reentrant angles, depressions,and the like or irregular protuberances (which may be difllcult to mreach) by subjecting the same to the abrasive action of relatively sharpand preferably coarse abrasive particles such as sand, chilled iron,alloy steels (of such composition as to render them hard) or stillharder abrasives such as the natgg ural and artificial abrasives,corundum, fused alumina, silicon carbide, boron carbide, tungsten Icarbide, and the like of which there is a large number.

An outstanding qualification of the'abrasive to be used, is that itshall quickly cut and remove the surface of the hardened steel object tobe examined, but it need not be a rapid-cutting abrasive with respect tothe hardened steel below.

In fact, only slight abrasion or wear upon such parts isusually'desirable, especially if the object has been partially orcompletely finished before the hardening operation. As will appearherein after, it is only necessary that the abrasive shall be harderthan the soft spots to be detected.

The application of the invention will be die on scribed with respect tothe examination of steel saw blades the surface of which, treated fortesting and examination purposes, is illustrated by the accompanyingdrawing, in which:

Fig. l is a plan vew of the surface of the blade; he and Fig. 2 is anenlarged cross section of the e in the plane 2-2 of Fig. 1.

The blades may be shaped in the usual manner, and then subjected to heattreatment in accordin ance with any customary practice. The hard= enedblade is subjected to a blast of compressed air, into which a constantstream of the granular abrasive, such as spent molding sand orpreferably a fairly coarse sharp sand 30 to 36 (mesh), 7t, is graduallyfed. The quantity of abrasive is preferably kept low, inasmuch as thisrenders the individual particles more effective on the one hand and onthe other avoids too great removal of the surface which is undertreatment. It also enables the operator more closely to observe thescoring or cutting action. Nevertheless, the surface is promptly anduniformly cleaned throughout or over such areas as experience maydetermine as most susceptible to soft spots.

If the cleaned surface is uniformly bright in appearance (due regardbeing taken of the shadow effects of uniform scratches or cuts,especially if they are deep) it indicates that the article is free fromsoft spots and has been uniformly hardened by the hardening treatment.On the other hand, if there are soft spots which in any place reach tothe surface, they are immediately manifest by the appearance of areas inwhich the sand blast has had a very different effect, usually resultingin producing a darker surface, which is also less directly reflective tolight, and hence duller in appearance. The size of the soft spot isindicated by the size of the dark area; and the degree of softness isindicated by the degree of darkness of the spot and by the uniformity ornon-uniformity of darkness throughout its area. The shape and size ofthe spot, (and its position relative to others) will give some furtherindication as to the probable depth or thickness of the spot.

A closer examination of the surface may be made microscopically ifdesired, and is especially applicable to the margins of the-softer spotsto detect. the causes of their occurrence. It may 110 also prove usefulwith respect to the degree of hardness of the properly hardened portionas well as of the soft portion of the article being tested.

Thus the cuts 1, 1', produced in the surface of the metal 2, may bewholly irregular, or, as indicated in Fig. 1, more or less parallel toeach other; but, if made by uniformly sized abrasive grains they areusually of approximately equal width. In the softer spots 3, 3, theabrasive grains penetrate deeper, as shown in Fig. 2, so that whilelight rays 4. are reflected from the fresh surfaces of the shallowercuts 1, rays 5 are absorbed or totally reflected from the deeper cuts1', thus making the latter appear dark when viewed, for example, by anobserver at the right hand side-of the figure.

With coarser abrasives and/or higher air pressures, the abrasion will bemore drastic and the individual cuts deeper. Conversely, with finerand/or lower air pressures, the cuts will be shallower and the materialremoved will be less. In any case, for accurate inspection, it ispreferable to employ a granular abrasive of relatively uniform grainsize, in order to make the individual cuts ofa more uniform and regularsize on those portions of the steel which are of uniform hardness.Otherwise, a combination of very coarse and very fine cuts or scratchesmay make examination difficult and lead to an incorrect interpretationof the results. Likewise, it is well to maintain a fairly uniform airpressure and rate of feed of abrasive grain while blasting a givenarticle.

The effect obtained by the invention may be attributed to thedifferential cutting action of an abrasive grain, under a uniformaverage pressure or impact, upon a hardened steel surface which it mayout (even though slightly) and upon a softer surface which it will cutdeeper, under the same conditions. This difference in depth of cutproduces a series of scorings which, though usually substantiallyidentical, exhibit the phenomenon of total reflection, resulting in theabsorption of light and produce in those areas of deeper cuts, an areaof greater total reflection (i. e. absorption) of light (especially whendirected transversely of the scorings) than those where only light,shallow cuts have been produced. Hence, only extremely small differencesin depth of cut in such surfaces are accompanied by marked contrastswhich may be readily observed upon only casual inspection.

- The hardened products in which soft spots are detected may of coursebe rehardened in the customary manner before further operations havebeen carried out upon them, thus saving the expenditure of labor uponarticles subsequently to be found defective and avoiding the output ofarticles which, though defective, are not suspected and may fail at acritical point in their subsequent operation or use.

It will be readily understood that the invention may likewise be appliedto objects which are predominantly soft for spots which are, bycomparison, hard.

I claim:

spots which comprises abrading or polishing the surface with an abrasivematerial which produces scores therein characterized by severallyexhibiting depths varying substantially in proportion to the relativesoftness of the surface, i1- luminating the same and observing the lighteffects exhibited by the surface indicating the relative degrees ofsoftness and hardness therein.

2. Method of testing heat hardened metal products for the detection ofsoft spots therein, which comprises the step of subjecting the surfaceof the same to the impact and cutting action of abrasive particles undera uniform, but yielding momentum and pressure, thereby to clean and cutthe surface in scores characterized by exhibiting depths varyingsubstantially in proportion to the relative softness of the surface,illuminating the same and observing the light effects ex-. hibited bythe surface indicating the relative degrees of softness and hardnesstherein.

3. Method of testing heat hardened steel products for the detection ofsoft spots therein, which comprises the step of subjecting the surfaceof the same to the action of abrasive particles of uniform size andunder a uniform but yielding pressure, which produces a series ofparallel scores characterized by exhibiting depths and widths, uniformin surfaces of uniform hardness and varying in proportion to therelative degrees of softness in surfaces which are not uniform,illuminating the same and observing the light effects exhibited by thesurface indicating the relative degrees of softness and hardnesstherein.

4. Method of testing heat hardened steel products for the detection ofsoft spots which comprises the steps of subjecting the surface of thesame to the impact and abrasion of a stream of abrasive particlescarried in a stream of air under uniform pressure, which producesscorings in said surface, substantially parallel and proportionate in'depth and width to the relative degree of softness thereof, illuminatingthe same, and observing the-relative degrees of light absorptionexhibited by the surface, indicating corresponding degrees of softness,if any, therein.

5. Method of testing heat hardened steed products for the detection ofsoft spots, which comprises the steps of subjecting the surface of thesame to the impact and abrasion of a uniform stream. of abrasiveparticles carried by a stream of air under uniform pressure, whichproduces scores in said surface, substantially parallel andproportionate in depth and width to the relative degrees of softnesspresented by the surface, illuminating the scored surface withsubstantially parallel light transversely of the scorings and observingthu relative degrees of light absorption (or total reflection) exhibitedby the scoring as indicating the relative depths produced and thecorresponding degrees of softness of said surface.

LESLIE E. HOWARD.

